Formation and Disproportionation of Xanthenols to Xanthenes and Xanthones and Their Use in Synthesis

Abstract

A facile and versatile strategy employing TiCl 4mediated cyclization followed by a Cannizzaro reaction has been developed for the synthesis of various xanthene derivatives. The reaction proceeded smoothly to afford both xanthenes/xanthones or their sulfur derivatives and tolerated a wide range of electronically diverse substrates. Using this methodology, pranoprofen was synthesized in three steps in 59% overall yield from commercially available starting materials.

Electrocatalytic synthesis: an environmentally benign alternative for radical-mediated aryl/alkenyl C(sp2)–C(sp3) cross-coupling reactions

“…Xanthene, an extremely important oxygen-containing tricyclic compound, is recognized as a useful activated alkyl radical precursor for the preparation of highly valuable complex molecules. 39 In 2022, Li et al established an electrochemically promoted regioselective C(sp 2 )–H/C(sp 3 )–H cross-coupling of indoles with xanthenes in an undivided cell (Scheme 20). 40 A series of C3-functionalized indoles were constructed in moderate to good yields without any metal catalyst or external chemical oxidant.…”

Esters as Both Alkylating and Acylating Reagents: PCl3‐Promoted Friedel‐Crafts Reaction in One‐Pot

“…Inspired by a handful of literatures [13][14][15] and our previous work [16] on the reductive alkylation reactions using aromatic aldehydes, we envisioned that the starting material containing both a aldehyde group and an ester group on the benzene ring may undergo the alkylation and acylation process in onepot. This is indeed the case.…”

Oxidation of BINOLs by Hypervalent Iodine Reagents: Facile Synthesis of Xanthenes and Lactones

“…[10] Since then, various methods have been developed to synthesize these compounds, [11] which mainly focus on exploring different substrates, designing novel catalysts and leveraging new technology. Taking typical research results in the last year as examples, the complex [(C 6 H 6 )(PCy 3 )(CO)-RuH] + BF 4 À was used as a catalyst for the reaction of phenols and aldehydes, [12] In(OTf) 3 was employed to catalyze the coupling of 1,4-quinones with oxindoles, [13] nano-capsule Fe 3 O 4 @Al 2 O 3 @SiO 2 @Fe 2 O 3 were prepared to catalyze the condensation of benzaldehyde and 2naphthol, [14] K 2 S 2 O 8 was used as a promoter to achieve the reaction of 2-aryloxy phenylacetylenes with phosphine oxides, [15] TiCl 4 was used for the cyclization of 2aryloxybenzaldehydes, [16] Cu(OAc) 2 was shown to catalyze the reaction of propargyl amines with 2-hydroxynaphthalene-1,4diones [17] and others. [18] Among the synthetic methods to prepare xanthene derivatives, the oxidation of BINOLs mediated by copper salt and amines is a straight way to synthesize binaphthyl-based xanthene derivatives.…”

“…The reaction cannot occur in water due to the poor solubility of BINOL and 2 a. A mixture solvent of water and DCE was also used, but the yield of 3 a was not increased (Table 1, entries [16][17]. Also different hypervalent iodine reagents, such as (diacetoxyiodo)benzene 2 b, [bis(trifluoroacetoxy)iodo]benzene 2 c and iodoxybenzene 2 d were screened, but the yield of 3 was not improved (Table 1, entries 18-20).…”